Romans 2:5

But after thy hardness and impenitent heart treasurest up for thyself wrath in the day of wrath and revelation of the righteous judgment of God.

The day of ... Thus Paul followed the teaching of the Saviour who made repeated reference to "the day of judgment" (Matthew 7:22; 11:22-24, etc.).

Impenitent heart ... shows the wrong response to God's goodness, the purpose of which was to lead men to repent, but which had been perverted by some who had accepted it as tacit approval of THEIR wickedness, and with the result of hardness and impenitence in their hearts. How paradoxical that the very goodness of God which should have produced penitence, as intended, produced instead an arrogant, hard-hearted impenitent, who by such misuse of God's goodness had treasured up for himself a terrible weight of wrath in the last day. The same paradox is evident in the influence of the gospel, as Paul said,

For we are a sweet savor of Christ unto God, in them that are saved, and in them that perish; to the one a savor from death unto death; and to the other a savor from life unto life (2 Corinthians 2:15,16).

Treasurest up ... God will reward iniquity. As Hodge noted,

"To treasure up" is to lay up little by little, a store of anything whether good or evil The abusers of God's goodness accumulate a store of wrath for themselves.[8]